Map Scale Calculator Tools? (Kelso)

Do you know of any good tools for converting a map’s graphic scale bar measurement to a representational fraction (RF)? Please share them! We often think of maps as 1:24,000 or 1:1,000,000 natural scale but more often than not a scale bar is the only indication of scale we have on a map. How to convert that back to the more familiar representational fraction?

What are the features and interface you’d like to see for such a tool?

Type in the number of units per distance (or distance per unit) and it’ll return the relational fraction. It does not do a very good job allowing you to type in both the units and the distance as variable. I hardly ever find scale bars on maps that are exactly an inch long. So involves some pre-math to get this tool to work.

Some example map scales and worked formula examples from Richard Layton (source).

1 inch equals 10 miles

1 inch = 10 miles

1 inch = 10 miles x 12 inches/foot x 5280 feet/mile

1 inch = 10 x 63360 inches = 633,600 inches

1:633,600

To convert from RF to Verbal Scale you convert the fraction to familiar units of measurements; for example:

1:250,000

1 inch = 250,000 inches

1 inch = 250,000 inches [d] 12 inches/foot = 20,833.3 feet

1 inch = 20,833.3 feet [d] 5280 feet/mile = 4 miles or

1 inch = 250,000 [d] 63360 inches/mile = 4 miles

1 inch equals 4 miles

[Note:[d] = divided by]

SOME COMMON SCALES. Here is a list of RF scales commonly used in the Map Collection and their equivalent Verbal Scales.

1:24,000- 1 in. = .379 mi.

1:62,500- 1 in. = .986 mi.

1:100,000 – 1 in. = 1.578 mi.

1:250,000- 1 in. = 4 mi.

1:500,000- 1 in. = 7.891 mi.

1:1,000,000 – 1 in. = 15.783 mi.

For example you want a map of Arizona on a 8 1/2 x 11 inch piece of paper. To allow for 1/2-inch margins the new sheet will then be 7 1/2 x 10 inches. Since Arizona’s north-south dimension, 395 miles, is slightly longer than its east-west dimension, 340 miles, we will place the longer north-south dimension along the longer 10-inch dimension of the paper. The next step is to compute the scales for both dimensions of the State. The smaller of the two scales will be the one we need.

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on Monday, December 15th, 2008 at 10:01 pm and is filed under Best practices, Mapping, Promote, Software.
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